Optical smoke detector with light scattering test device

ABSTRACT

An optical smoke and like particle detector housing in which light from a lamp is protected along one axis and scattered by particles along a second axis to a photocell has a particle simulating device for testing the operativeness of the cell and its associated alarm circuit. The particle simulating device comprises a thin wire mounted on a bell crank manually operated outside the detector housing to swing the wire through the detection zone at the intersection of the lamp and photocell axes so as to scatter light from the lamp to the cell in the same way and amount as particles in the zone.

United States Patent Marsocci Feb. 25, 1975 54] OPTICAL SMOKE DETECTORWITH 3,234,846 2/1366 LIV/1001C 356/243 3,505,529 4 1 70 v, 1 356/207LIGHT SCATTERING TEST DEVICE 3,702,734 11/1972 Lindahl et al 356/207Angelo August Marsocci, West Warwick, RI.

Assignee: Electro Signal Lab, Inc., Rockland,

Mass.

Filed: July 25, 1973 Appl. No.: 382,521

Inventor:

US. Cl. 356/103, 250/574, 340/237 S, 356/207 Int. Cl. G0ln 21/00, GOln21/12 Field of Search 356/103, 104, 207, 243; 340/237 S; 250/574References Cited UNITED STATES PATENTS Primary Examiner-Vincent P.McGraw Attorney, Agent, or FirmJames H. Grover [57] ABSTRACT An opticalsmoke and like particle detector housing in which light from a lamp isprotected along one axis and scattered by particles along a second axisto a photocell has a particle simulating device for testing theoperativeness of the cell and its associated alarm circuit. The particlesimulating device comprises a thin wire mounted on a bell crank manuallyoperated outside the detector housing to swing the wire through thedetection zone at the intersection of the lamp and photocell axes so asto scatter light from the lamp to the cell in the same way and amount asparticles in the zone.

' 5 Claims, 3 Drawing Figures OPTICAL SMOKE DETECTOR WITH LIGHTSCATTERING TEST DEVICE BACKGROUND OF THE INVENTION In optical detectorsof smoke and like fluid borne particles of the reflection type a beam oflight is directed from an exciter lamp along a path or axis usuallylocated within a dark chamber having ports to admit air but excludeambient light. Light scattered from particles in the light path isviewed by a photocell which responds by sending a signal to anassociated alarm circuit. Typically the optical system, photocell andalarm circuit are designed to respond to a smoke density of betweenapproximately 2 to percent obscuration per foot; that is, a smokedensity which in one foot will attenuate the light intensity from 2 to10 percent.

Owing to the aging of the lamp, photocell and alarm circuit componentsthe alarm point (in smoke density percentage) of the detector will driftover a period of time. the drift usually being upward in percentagecorresponding to a decrease in sensitivity of the detector. When thedetector ceases to be responsive to smoke densities in excess of 10percent for example lethal quantities of smoke and accompanying toxicgases can accumulate and the causative fire may spread without warning.In both industrial and residential buildings smoke detectors areexpected to function properly without attention and years may passduring which the detector is allowed to drift to an inadequatelysensitive state.

Accordingly one object of the present invention is to provide a simpleinexpensive test, not merely of the operativeness of a particulardetector component such as the photocell, but rather of the ultimatefunction of the detector, namely to alarm in response to a predeterminedsmoke density.

A further object is to provide a test which is independent of theposition of the filament in the exciter lamp and of consequentvariations of the location of the light path in the dark chamber.

SUMMARY OF THE INVENTION According to the invention an optical particledetector comprises a housing enclosing a dark chamber; a lamp mounted onthe housing to direct on a path into the chamber; a photosensitivedevice on the housing viewing the light path and responsive to lightscattered by particles in the path; and a particle simulating membermovably mounted on the housing and having a portion movable through thelight path at a zone scattering a calibrated intensity of light to thedevice independently of the presence and accumulation of particlesbetween the lamp and device.

DRAWING FIG. I is a plan view shown partly in section of an opticalsmoke detector with a testing device according to the invention;

FIG. 2 is a section on line 22 of FIG. I; and

FIG. 3 is a section on line 3--3 of FIG. 2.

DESCRIPTION As shown in FIG. I an optical smoke detector comprises ahousing with bottom and top walls I and 2 and a circular side wall 3.Porous foam pads 4 in ports through the side wall admit air and airborne particles like smoke while excluding light from a dark chamber 6which on one side is closed by an optical block 7 similarly as isdescribed in U.S. Pat. No. 3,723,747. The optical block mounts anexciter lamp 8 such as Hudson or GE No. 1 type 755 whose filament 9 is astraight coil. A lamp lens 11 beams a cone of light from the lamp on apath through a passage 12 in the block along an axis Al across the darkchamber 6. A detector cell 13 views the chamber through a second passageI4, a cell lens 16 along an axis A2 120 from the lamp axis Al. Alsomounted in the optical block 7 is a compensating photocell 14 describedin said US. Pat. No. 3,723,747 which receives light directly from thelamp 9 balances certain aging effects in the smoke cell 13. When smoke,for example, enters the dark chamber 6 through the foam ports 4, smokein the detection or intersection zone Z of the light path on axis A1 andthe cell viewing path on axis A2 scatters light to the smoke cell 13causing it to respond with a photoelectric signal. The smoke cell isconnected through terminals 16 to an alarm circuit board 18, thecompensating cell 14 being connected to the board through terminals 17.The lamp, cells and circuit are designed to respond to a predeterminedsmoke obscuration percentage as previously defined in BACKGROUND OF THEINVENTION, the preferred percentage being close to 2 percent, and up to10 percent being allowable but increasingly less desirable. The desiredor predetermined level of detector response to the amount of lightscattered from smoke of such obscuration density may be calibrated aslight intensity or the corresponding smoke obscuration percentage.

According to the invention the detector as a whole is tested under thesame conditions as with the presence of the predetermined level of smokein the chamber 6, by scattering a calibrated amount of light from thelight path A1 at the intersection zone Z back along the cell viewingpath A2 with a particle simulator 20. The simulator comprises a wirebell crank having a finger grip 21 outside the circular chamber wall 3,an axial shaft portion 22 with a central U-bend 23 and a relatively finewire 24 spot welded to its inner end in the dark chamber 6. The shaft 2is pivotally held in snap-in sockets formed in bosses 26 molded in anddepending from the plastic top wall 2. The U-bend portion 23 isangularly offset approximately 25 from the fine wire and limits rotationof the bell crank by engagement with a set screw 25 threaded through thetop wall 2. In normal operation the fine wire 24 hangs vertically out ofthe light path on axis A1 and the smoke detection zone Z, as shown inFIGS. 2 and 3.

The fine wire 24 is of a diameter and surface area in proportion to thecross section of the conic light beam on axis A1 at the zone Z such thatit effectively scatters a calibrated amount of light corresponding tothat scattered by smoke of 2 to 10 percent obscuration density whenswung through the zone Z from the solid line position in FIG. 3 to thephantom position 24 Preferably the calibrated light intensity isequivalent to 5 to 10 percent smoke since detector components are notpresently expected to maintain an initial sensitivity to 2 percent smokefor several years and yet are acceptable at approximately 5 to 10percent smoke level sensitivities. With a No. I type 755 lamp 8, aClairex type 5M7 smoke cell 13, and light and cell passages of aboutonethird inch a fine wire diameter of 34 gauge or about th inch diameterscatters a calibrated intensity of light from the detection zone Z tothe cell 13 corresponding to the range of 2 to percent smoke. Preferablythe whole particle simulator including the fine wire 24 has a dull blackoxide finish with a light waxing. preferably the operability test ismade by slowly swinging the particle simulator completely through thelight path at the intersection zone Z until the U-bend hits the setscrew25 after the fine wire has substantially passed through the zone. Theset screw can be adjusted to stop the fine wire at a central position inthe zone, but because the location of the filament 9 in the lamp 8varies, the location of the light axis A] and the center of theintersection zone Z will shift from lamp to lamp. However, with closetolerance of filament position or by lamp selection the fine wire may bestopped in the zone.

lt should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

I claim: 1. An opticle particle detector comprising: a housing enclosinga dark chamber; a lamp mounted on the housing and means to direct lighton a confined path into the chamber; a photosensitive device on thehousing viewing the light path and responsive to light scattered byparticles in the light path; and

a particle simulating member having a light scattering surface ofpredetermined width and of extent at least substantially as great as thecross section of the light beam, the member being mounted on the housingfor continuous, unobstructed movement through positions in the lightbeam to and through a position of predetermined light scatter withoutselection of the position by the operator, so that during such movementa calibrated intensity of light will be scattered to the device.

2. particle detector according to claim 1 wherein the photoelectricdevice is responsive to a calibrated intensity of light scattered fromthe path to the device by a predetermined particle density to produce analarm signal, and said particle simulating member being of a size toscatter light of the calibrated intensity.

3. A particle detector according to claim 1 wherein the simulatorcomprises a rotatable bell crank with a finger grip at one end and alight scattering flag at its other end.

ie t zqt e es qr e rr qrs tL l claim 3 wherein the bell crank has anintermediate arm, and an adjustable stop limits movement of theintermediate arm.

5. A detector according to claim 1 wherein the light scattering surfaceis cylindrical.

l l =l=

1. An opticle particle detector comprising: a housing enclosing a darkchamber; a lamp mounted on the housing and means to direct light on aconfined path into the chamber; a photosensitive device on the housingviewing the light path and responsive to light scattered by particles inthe light path; and a particle simulating member having a lightscattering surface of predetermined width and of extent at leastsubstantially as great as the cross section of the light beam, themember being mounted on the housing for continuous, unobstructedmovement through positions in the light beam to and through a positionof predetermined light scatter without selection of the position by theoperator, so that during such movement a calibrated intensity of lightwill be scattered to the device.
 2. a particle detector according toclaim 1 wherein the photoelectric device is responsive to a calibratedintensity of light scattered from the path to the device by apredetermined particle density to produce an alarm signal, and saidparticle simulating member being of a size to scatter light of thecalibrated intensity.
 3. A particle detector according to claim 1wherein the simulator comprises a rotatable bell crank with a fingergrip at one end and a light scattering flag at its other end.
 4. aparticle detector according to claim 3 wherein the bell crank has anintermediate arm, and an adjustable stop limits movement of theintermediate arm.
 5. A detector according to claim 1 wherein the lightscattering surface is cylindrical.